This invention is related to the field of biofouling release coatings for use in industrial, commercial or military marine and freshwater applications. In particular, this invention relates to a method for regenerating a biofouling release coating which has decreased release efficacy due to depletion or lack of an incorporated oil.
Damage to underwater power cables, ships, and the like due to colonization of their surfaces by organisms (including, but not limited to, barnacles) has serious economic consequences in marine and freshwater industries. Antifouling and fouling release coatings have been developed to prevent or reduce biofouling, and to loosen the strength of the attachment of marine organisms to make cleaning surfaces easier. There are many commercial foul release coatings including, for example, GE EXSIL(copyright) 2200. However there have been no reports of renewal methods for these coatings.
There has been a continuing need in the coatings industry for new methods for increasing the useful life of fouling release and antifouling coatings. At present, the useful lifetime of a copper ablative antifouling coating is approximately three years, after which time the coating must be removed from the hull and reapplied. It is estimated that the effective life span of silicone fouling release coatings is about 5-7 years.
The release characteristics of silicone fouling release coatings are known to be significantly enhanced by the addition of oils such as mineral oil and silicone oils. Barnacle adhesion measurements on fouling release coatings substantiate that removal of fouling requires less work when the silicone topcoat has been prepared with incorporated oils. For example, silicone oils such as dimethyl silicone oils, phenyl-modified silicone oils, and polyether-modified silicone oils have been incorporated into biofouling release coatings.
Unfortunately, these additives tend to diffuse out of the coating during use and are thus rapidly depleted. The depleted coatings lose their enhanced foul-release properties, and consequently their effectiveness is reduced. Depletion of the additive therefore limits the useful life of the coating, necessitating periodic removal and reapplication of a new silicone biofouling release coating. A recoat technology for these coatings which does not require complete removal and reapplication of the coating would significantly reduce life-cycle costs and enhance the attractiveness of these coatings to the power utility, military, industrial, and commercial markets.
To forestall the rapid oil-depletion of oil-containing biofouling release coatings, larger amounts of oil have been incorporated into these coatings. This solution to the problem does curtail the rapid depletion of the oil, but unfortunately it tends to severely impair the mechanical properties of the coatings, particularly tear strength and abrasion resistance. Increasing the original additive content of biofouling release coatings, therefore, does not provide a workable method of increasing the life of the coatings.
Silicone biofouling release coatings made without additives also have been used to make cleaning surfaces of organisms easier, but they are not as effective as coatings with incorporated oils. A method for enhancing the properties of these coatings, as well as restoring the enhanced release properties of older coatings originally containing additives is highly desirable.
The present invention relates to a method of introducing enhanced biofouling release properties to an intact biofouling release coating, which method comprises exposing the surface of the biofouling release coating to a restorative compound for a time sufficient to effect enhancement of biofouling release properties.
In a further aspect, the present invention relates to a kit for the enhancement of the biofouling release properties of an intact biofouling release coating, said kit comprising a container containing a restorative compound suitable for said enhancement.
In yet another aspect, the present invention relates to a kit for the enhancement of the biofouling release properties of an intact biofouling release coating, said kit comprising a container containing a biofouling release coating, and a container containing a restorative compound suitable for said enhancement.
The term xe2x80x9coil-depletedxe2x80x9d referring to release coatings will be used in this application to denote any biofouling release coating, whether manufactured with or without incorporated oils, which has been depleted of the oil additive or lacks the oil additive, and therefore has a reduced effectiveness compared to coatings containing the oil additive. It is not to be construed as limited solely to coatings which were manufactured containing oil and have subsequently been depleted of the oil.
The biofouling release coatings which may be enhanced by the present invention include generally any coating into which a restorative compound may be incorporated for enhancement of biofouling release properties. The present invention is particularly applicable to release coatings which include a conventional one-part or two-part RTV composition, preferably a two-part composition. It may comprise at least one reactive silicone, at least one condensation catalyst and at least one crosslinking agent.
The reactive silicone is preferably at least one of a polydialkylsiloxane, a polydiarylsiloxane, or a polyalkylarylsiloxane typically of the formula 
wherein each R1 is a hydroxyl radical or 
each R2 is independently a hydrocarbon or fluorinated hydrocarbon radical, each R3 and R4 is independently a hydrocarbon radical, a is 0 or 1, and m has a value such that the viscosity of said compound under ambient temperature and pressure conditions is up to about 50,000 centipoise. Illustrative hydrocarbon radicals are C1-20 alkyl, C6-20 aryl and alkaryl, vinyl, isopropenyl, allyl, butenyl and hexenyl, with phenyl, C1-4alkyl and especially methyl being preferred. An illustrative fluorinated hydrocarbon radical is 3,3,3-trifluoropropyl. Preferably, each R2, R3 and R4 is alkyl and preferably methyl. The biofouling release coatings may comprise two or more reactive silicones, differing in average molecular weight, which may afford a bimodal composition having performance advantages over a simple monomodal composition.
The condensation catalyst may be any of those known to be useful for promoting condensation curing of an RTV material. Suitable catalysts include tin, zirconium, titanium, and aluminum compounds as illustrated by dibutyltin dilaurate, dibutyltin diacetate, dibutyltin methoxide, dibutyltin bis(acetylacetonate), 1,3-dioxypropane-titanium bis(acetylacetonate), titanium naphthenate, tetrabutyl titanate, zirconium octanoate, and aluminum acetylacetonate. Various salts of organic acids with such metals as lead, iron, cobalt, manganese, zinc, antimony and bismuth may also be employed. For most purposes, the tin and titanium compounds are preferred.
As crosslinking agents, trifunctional (T) and tetrafunctional (Q) silanes are useful, the term xe2x80x9cfunctionalxe2x80x9d in this context denoting the presence of a silicon-oxygen bond. They include such compounds as methytrimethoxysilane, methyltriethoxysilane, 2-cyanoethyltrimethoxysilane, methyltriacetoxysilane, tetraethyl silicate and tetra-n-propyl silicate. The Q-functional compounds, i.e., tetraalkyl silicates, are often preferred.
The coating may contain other constituents, including reinforcing and extending (non-reinforcing) fillers. Suitable reinforcing fillers are commercially available in the form of relatively large aggregated particles typically having an average size significantly greater than about 300 nanometers (nm). The preferred fillers are the silica fillers, including fumed silica and precipitated silica. Those two forms of silica have surface areas in the ranges of 90-325 and 8-150 m2/g, respectively.
The reinforcing filler is most often pretreated with a treating agent to render it hydrophobic. Typical treating agents include cyclic silicones such as cyclooctamethyltetrasiloxane and acyclic and cyclic organosilazanes such as hexamethyidisilazane, 1,3-divinyl-1, 1,3,3-tetramethyidisilazane, hexamethylcyclotrisilazane, octamethyl cyclotetrasilazane, and mixtures thereof. Hexamethyldisilazane is often preferred.
Non-reinforcing fillers include titanium dioxide, lithopone, zinc oxide, zirconium silicate, iron oxides, diatomaceous earth, calcium carbonate, glass fibers or spheres, magnesium oxide, chromic oxide, zirconium oxide, aluminum oxide, crushed quartz, calcined clay, talc, kaolin, asbestos, carbon, graphite, cork, cotton and synthetic fibers.
The proportions of the constituents of the silicone component may be varied widely. The amount of filler is generally about 5-200 parts and preferably about 10-150 parts by weight per 100 parts of reactive silicone. Catalysts and crosslinkers are generally present in the amounts of about 0.001-2.5% and about 0.25-5.0% by weight respectively, based on the combination of reactive silicone and filler.
Restorative compounds which may be used in connection with the present invention include oils such as polyorganosiloxanes (e.g., polyalkylsiloxanes, organic-compatible siloxanes, polymethyl-phenylsiloxanes, polydiphenylsiloxanes, hydrophilic siloxanes, carbinol-functional siloxanes, and related compounds); crude oil products (e.g., paraffin wax, petroleum waxes, petrolatum, liquid paraffin, and greases); and fats, oils and waxes.
Oil-depleted biofouling release coatings may be restored by applying the restorative compound to the release coating surface. Such application may be by soaking, dipping, spraying, wiping, brushing, coating or otherwise exposing the coating surface to the desired restorative compound. During the application process, it is desirable to maintain the restorative compound in contact with the coating for a period of time sufficient to ensure adequate uptake of the restorative compound by the coating. The optimum period will vary according to a number of factors, including the identity and condition of the coating, the identity of the restorative compound, etc. The best contact time period for a given set of conditions may be readily determined by one of ordinary skill. A preferred period is at least about 10 hours, more preferably from about 10 to about 90 hours, and most preferably from about 24 to about 72 hours. Sufficient volumes of restorative compound to completely cover or immerse the surface of the coating are desirable, but not necessary. After treatment, the surface may be wiped dry, if desired. Any excess restorative compound may be recovered from the wipe for reuse by means known in the art.
The restorative compound useful in the present invention may be sold in the form of a kit, i.e., in a suitable container (e.g., a drum, can, carton, etc.), optionally with instructions for use being present in the kit, for example attached to or in association with the container. The kit may also comprise a container having a biofouling release coating, preferably compatible with the restorative compound.
The invention will be illustrated by the following non-limiting Examples.